1. Field of the Invention
The invention is directed to purified and isolated novel human thymic stromal lymphopoietin (TSLP) polypeptides and fragments thereof, the nucleic acids encoding such polypeptides, processes for production of recombinant forms of such polypeptides, antibodies generated against these polypeptides, fragmented peptides derived from these polypeptides, and uses thereof
2. Description of Related Art
Although B cell development has been extensively studied, there still remain gaps in the pathway leading from hematopoeitic stem cells to mature B cells. It is recognized that cytokines influence and play a critical role in B cell development and growth. Known cytokines that influence B cell development include IL-2, IL-4, IL-5, IL-6, IL-7, IFN-gamma, and granulocyte-macrophage colony-stimulating factor (GM-CSF).
In recent years, a novel murine growth factor, designated thymic stromal lymphopoietin (TSLP), has been shown to play a role in B cell development and maturation. The cytokine activity of murine TSLP is very similar to that of IL-7, which is required during proliferation and survival of pre-B cells (Janeway et al., Immuno Biology 2nd Ed. (1996)). Both of these cytokines have been shown to sustain NAG8/7 cells (Friend et al., Exp. Hematol., 22:321-328 (1994)) and support B lymphopoiesis. In addition, mature B lymphocytes fail to develop in the absence of either IL-7 or murine TSLP. Moreover, it has been shown that murine TSLP can replace IL-7 in sustaining B cell proliferative responses (Ray et al., Eur. J. Immunol., 26:10-16 (1996)). Thus, in the mouse system, TSLP has a significant function in B cell development.
Like IL-7, murine TSLP can also costimulate thymocytes and mature T cells (Friend et al., Exp. Hematol., 22:321-328 (1994)). Studies with IL-7 receptor (IL-7R) knockout mice indicate that IL-7, TSLP, or both play a crucial role in controlling the rearrangement of the T cell receptor-gamma (TCRγ) locus, presumably by mediating accessibility of the TCRγ genes to the VDJ recombinase (Candeias et al., Immunology Letters, 57:9-14 (1997)). Thus, murine TSLP also plays a significant role in T-cell development.
Murine TSLP receptors and IL-7 receptors both use the IL-7R α-chain as part of their signaling complexes (Levin et al., J. Immunol., 162:677-683 (1999)). Despite the common IL-7R a-chain, however, IL-7 and TSLP appear to mediate their lymphopoietic effects through distinct mechanisms. IL-7 induces activation of Stat5 and the Janus family kinases Jak1 and Jak3, whereas murine TSLP induces activation of Stat5, but not any of the known Janus family kinases (Levin et al., J. Immunol., 162:677-683 (1999)).
Given the important function of murine TSLP and the significance of its role in B cell and T cell development and maturation in the mouse system, there is a need in the art to identify and isolate human TSLP and to study its role in human B cell and T cell development and maturation. In addition, in view of the continuing interest in lymphocyte development and the immune system, the discovery, identification, and roles of new proteins, such as human TSLP and its receptors, are at the forefront of modern molecular biology, biochemistry, and immunology. Despite the growing body of knowledge, there is still a need in the art for the identity and function of proteins involved in cellular and immune responses.
In another aspect, the identification of the primary structure, or sequence, of an unknown protein is the culmination of an arduous process of experimentation. In order to identify an unknown protein, the investigator can rely upon a comparison of the unknown protein to known peptides using a variety of techniques known to those skilled in the art. For instance, proteins are routinely analyzed using techniques such as electrophoresis, sedimentation, chromatography, sequencing and mass spectrometry.
In particular, comparison of an unknown protein to polypeptides of known molecular weight allows a determination of the apparent molecular weight of the unknown protein (T. D. Brock and M. T. Madigan, Biology of Microorganisms, pp.-76-77, Prentice Hall, 6d ed., (1991)). Protein molecular weight standards are commercially available to assist in the estimation of molecular weights of unknown protein (New England Biolabs Inc. Catalog:130-131 (1995)); (J. L. Hartley, U.S. Pat. No. 5,449,758). However, the molecular weight standards may not correspond closely enough in size to the unknown protein to allow an accurate estimation of apparent molecular weight. The difficulty in estimation of molecular weight is compounded in the case of proteins that are subjected to fragmentation by chemical or enzymatic means, modified by post-translational modification or processing, and/or associated with other proteins in non-covalent complexes.
In addition, the unique nature of the composition of a protein with regard to its specific amino acid constituents results in unique positioning of cleavage sites within the protein. Specific fragmentation of a protein by chemical or enzymatic cleavage results in a unique “peptide fingerprint” (D. W. Cleveland et al., J. Biol. Chem. 252:1102-1106 (1977); M. Brown et al., J. Gen. Virol. 50:309-316 (1980)). Consequently, cleavage at specific sites results in reproducible fragmentation of a given protein into peptides of precise molecular weights. Furthermore, these peptides possess unique charge characteristics that determine the isoelectric pH of the peptide. These unique characteristics can be exploited using a variety of electrophoretic and other techniques (T. D. Brock and M. T. Madigan, Biology of Microorganisms, pp. 76-77, Prentice Hall, 6d ed. (1991)).
Fragmentation of proteins is further employed for amino acid composition analysis and protein sequencing (P. Matsudiara, J. Biol. Chem., 262:10035-10038 (1987); C. Eckerskorn et al., Electrophoresis, 9:830-838 (1988)), particularly the production of fragments from proteins with a “blocked” N-terminus. In addition, fragmented proteins can be used for immunization, for affinity selection (R. A. Brown, U.S. Pat. No. 5,151,412), for determination of modification sites (e.g. phosphorylation), for generation of active biological compounds (T.D. Brock and M. T. Madigan, Biology of Microorganisms, 300-301 (Prentice Hall, 6d ed., (1991)), and for differentiation of homologous proteins (M. Brown et al., J. Gen. Virol., 50:309-316 (1980)).
In addition, when a peptide fingerprint of an unknown protein is obtained, it can be compared to a database of known proteins to assist in the identification of the unknown protein using mass spectrometry (W.J. Henzel et al., Proc. Natl. Acad. Sci. USA 90:5011-5015 (1993); D. Fenyo et al., Electrophoresis, 19:998-1005 (1998)). A variety of computer software programs to facilitate these comparisons are accessible via the Internet, such as Protein Prospector (Internet site: prospector.uscf.edu), MultiIdent (Internet site: www.expasy.ch/sprot/multiident.html), PeptideSearch (Internet site: www.mann.embl-heiedelberg.de . . . deSearch/FR_PeptideSearchForm. html), and ProFound (Internet site: www.chait-sgi.rockefeller.edu/cgi-bin/prot-id-frag.html). These programs allow the user to specify the cleavage agent and the molecular weights of the fragmented peptides within a designated tolerance. The programs compare these molecular weights to protein molecular weight information stored in databases to assist in determining the identity of the unknown protein. Accurate information concerning the number of fragmented peptides and the precise molecular weight of those peptides is required for accurate identification. Therefore, increasing the accuracy in determining of the number of fragmented peptides and the precise molecular weight should result in enhanced likelihood of success in the identification of unknown proteins.
In addition, peptide digests of unknown proteins can be sequenced using tandem mass spectrometry (MS/MS) and the resulting sequence searched against databases (J. K. Eng, et al., J. Am. Soc. Mass Spec. 5:976-989 (1994); M. Mann and M. Wilm, Anal. Chem., 66:4390-4399 (1994); J. A. Taylor and R. S. Johnson, Rapid Comm. Mass Spec., 11:1067-1075 (1997)). Searching programs that can be used in this process exist on the Internet, such as Lutefisk 97 (Internet site: www.lsbc.com:70/Lutefisk97.html), and the Protein Prospector, Peptide Search and ProFound programs described above. Therefore, adding the sequence of a gene and its predicted protein sequence and peptide fragments to a sequence database can aid in the identification of unknown proteins using tandem mass spectrometry.
Thus, there also exists a need in the art for polypeptides suitable for use in peptide fragmentation studies, for use in molecular weight measurements, and for use in protein sequencing using tandem mass spectrometry.